In a manufacture of a semiconductor device, to meet recent demands for higher density and higher integration degree, a circuit arrangement tends to have a multilayer interconnection structure. Therefore, a technique that forms a buried portion for electrically connecting layers to each other through a contact hole for connecting a lower semiconductor substrate to an upper wiring layer, or through a via hole for connecting a lower wiring layer to an upper wiring layer becomes important.
In order to form a contact between a polycrystalline silicon layer or an underlying Si substrate and an alloy or metal used to fill the contact hole or the via hole, a Ti film is formed at an inner side of the contact hole or the via hole before filling up the contact hole or the via hole.
Conventionally, the Ti film is formed by physical vapor deposition (PVD). However, along with a demand for miniaturization and higher integration of the devices, chemical vapor deposition (CVD) having a better step coverage has been widely used recently.
As for a technique for forming a Ti film by using CVD, there is suggested a technique for forming a Ti film using plasma CVD (e.g., Japanese Patent Laid-open Application No. 2003-313666). Here, TiCl4 gas, H2 gas and Ar gas as a film forming gas are introduced into a chamber through a shower head, and a semiconductor wafer as a substrate to be processed is heated to a predetermined temperature while being mounted on a susceptor having therein a heater. A plasma of the above gases is produced by a high frequency power applied to parallel plate electrodes, and TiCl4 gas and H2 gas react with each other.
When a Ti film is formed by employing plasma CVD, an unwanted film is formed in the chamber, so that the interior of the chamber which has been previously used for the Ti film formation is cleaned by ClF3 gas. In order to prepare the chamber for a next Ti film formation, a pre-coating process for forming a Ti film on an inner wall of the chamber, the susceptor and the shower head is performed by using TiCl4 gas and H2 gas at a temperature same as that in a Ti film forming process. Thereafter, a Ti film is formed on a semiconductor wafer in the manner described above.
Conventionally, as for a material forming a susceptor, an AlN as ceramic having a high thermal conductivity is widely used. When cleaning is performed by using ClF3 gas, an AlF-based material AlFx (x being a natural number) is generated through the reaction between AlN and ClF3. Further, the AlF-based material is sublimated and adhered to a surface of a shower head during the pre-coating process. The AlF-based material, however, has lower adhesivity. Therefore, even if a Ti film is pre-coated on the AlF-based material, the pre-coated film may be peeled off during a film forming process, which may cause generation of particles. Moreover, the pre-coated film may be reduced by a film forming gas during the film forming process, so that the AlF-based material in a space formed between the surface of the shower head and the pre-coated film can be eluted into the film forming gas. In that case, the wafer surface may be contaminated by the AlF-based material released into the film forming gas.
Further, during the pre-coating process, Ti contained in the film forming gas reacts with Ni contained in the chamber or the shower head, thereby forming NiTi. The NiTi may be incorporated into the pre-coated film and be eluted during the film forming process, which may lead to contamination of the wafer surface.